Global Management of Local Link Power Consumption

ABSTRACT

Power reduction in links, such as transmitters and receivers, based upon global decisions such as the data transmission frequencies, communications media, and traffic types associated with links, is disclosed. In particular, embodiments take advantage of high-level decisions by reconfiguring internal circuits of transmitters and receivers of links to reduce power consumption. At the global level, a decision determines the links that are active, the data frequency at which the links operate, and the media through which the links transmit the data. At the local level, the links receive the decisions and reconfigure circuitry automatically to minimize power based upon the decisions. In some embodiments, the links may receive the decisions in the form of power modes. In further embodiments, the links may receive settings such as on/off settings, data frequency settings, and traffic/media settings, the combination of which indicates power modes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/743,653, entitled “Global Management of LocalLink Power Consumption”, attorney docket number AUS920030892US1(4021),filed Jan. 22, 2003, the disclosure of which is incorporated herein inits entirety for all purposes.

BACKGROUND

The present invention is in the field of communications channels, orlinks. More particularly, the present invention relates to methods andarrangements for power reduction in links, such as transmitters andreceivers, based upon global decisions such as the data transmissionfrequency, communications media, and traffic type associated with thelinks.

Communication systems typically include logic and hardware to transmitdata from an origin to a destination. In particular, communicationsystems have routing or switching logic to make high-level decisionsthat select ports, routes, and media for transmitting the data.Communication systems also include links, each having a transmitter, amedium, and a receiver, to transmit the data in response to thosehigh-level decisions.

The origin clocks the data originally. Then, each intermediate link, ormore specifically, the link's transmitter typically clocks the data andtransmits to the link's receiver or the destination.

Devices such as routers typically access a network identification(NETID) for the data transmission to determine the destination andcalculate the route to the destination through intermediate links basedupon a routing protocol and a routing table that includes informationabout the communication system's topology. The routing protocoldynamically determines routing for the data transmission, taking intoconsideration changing conditions of the communication network such asunavailable links. Routing tables, for instance, may associate linkswith ports, or port numbers, through which the data transmission shouldbe routed.

Upon determining the port for the data transmission, the transmission isrouted through that port to the destination or another, intermediatedestination. Some of the more complex routers, such as routers for supercomputers, may also select a medium through which the transmitter andreceiver will transmit the data.

The transmitters and receivers may consume more power depending upon thedata transmission and the media through which the data transmission isrouted. In particular, data transmissions at higher data frequencies,with difficult data traffic types or patterns, via long media, and/orvia lossy media, require amplifiers and complex, mixed-signal circuitry.The amplifiers and complex, mixed-signal circuitry improve or maximizethe sampling window for bits of data in the data transmission tomaintain an acceptable bit error rate (BER), i.e., the number ofmisinterpreted bit values for the data transmission.

Higher data frequencies require internal circuits of transmitters andreceivers to operate at high clock frequencies and, thus, high voltagelevels, to sample and re-transmit the data in each intermediate link.Further, when the clock frequencies of a transmitter and receiver pairhave differences in phase that change over time, often referred to asspread spectrum signaling, the receiver may include a clock and datarecovery (CDR) loop with second and, possibly, third order frequencytracking circuits running at high internal frequencies.

Similarly, demanding traffic types, which include patterns that do notoften switch between logical ones and zeros or that switch between onesand zeros in irregular or sporadic patterns, require complex internalcircuits of transmitters and receivers that may operate at high clockfrequencies to capture the relatively few transitions. The phase of thesampling clock is adjusted based upon the phase of the data signal asdetermined from those relatively few transitions.

With regards to long and/or lossy media, the amplitude of the datatransmission may attenuate in a frequency-dependent manner.Amplification and pre-emphasis by the transmitter as well asamplification and equalization by the receiver accentuate certainfrequencies to increase the sampling window. Other circuitry such asinternal loop filters may be more complex when the media is long and/orlossy.

The amplification and complex, mixed-signal circuitry, however,significantly increase the overall power consumption for thecommunication system. For example, serial links within a largeinterconnect system such as a super computer may consume 20 to 37% oftotal power consumption.

Further, the amplifiers and complex, mixed-signal circuitry continue tooperate at full power even when such circuitry is unnecessary. Forexample, a high-level decision may make a link inactive or switch themedia for the link from a long medium that requires the complex,mixed-signal circuitry, to a shorter medium that does not require suchcircuitry.

Thus, there is a need for methods and arrangements for power reductionin link circuits such as transmitters and receivers based upon global,or high-level, decisions such as the activity, data transmissionfrequency, communications media, and traffic type associated with links.

SUMMARY

One embodiment provides an apparatus to retransmit a data transmissionbetween a first device and a second device via intermediate links. Theapparatus comprises a global link control to determine ports of theintermediate links to transmit the data transmission to a destinationdevice; to determine an activity assignment for the ports of themultiple links based upon forwarding logic, wherein determining theactivity assignment comprises determining a data frequency, traffictype, and medium type for the data transmission; and to transmit acontrol signal with the activity assignment to local link controls ofthe intermediate links associated with the data transmission. Theapparatus also comprises a first port and a second port. The first portmay communicatively couple with a transmitter of the first device via afirst data transmission medium to form a first intermediate link of theintermediate links. The first port may comprise a first link circuit tocouple to the first data transmission medium, to receive the datatransmission from the first device, and a first local link control ofthe local link controls responsive to the control signal from the globallink control to configure the first link circuit to operate in a firstpower mode of multiple power modes associated with the first linkcircuit based upon the activity assignment. The second port maycommunicatively couple with a receiver of the second device via a seconddata transmission medium to form a second intermediate link of theintermediate links and with the first port to retransmit the datatransmission. The second port may comprise a second link circuit tocouple to the second data transmission medium, to transmit the datatransmission to the second device, and a second local link control ofthe local link controls responsive to the control signal from the globallink control to configure the second link circuit to operate in a secondpower mode of multiple power modes associated with the second linkcircuit based upon the activity assignment.

Another embodiment provides an apparatus. The apparatus may compriseforwarding logic to associate ports with multiple links between anorigin and a destination for a data transmission to transmit the datatransmission via the multiple links to the destination, each of themultiple links to comprise a first port with a transmittercommunicatively coupled with a receiver of a second port via a datatransmission medium. The apparatus may also comprise a global linkcontrol coupled with the forwarding logic to determine an activityassignment for the ports of the multiple links based upon the forwardinglogic, wherein determining the activity assignment comprises determiningthe data frequency, traffic type, and medium type for the datatransmission to transmit a control signal to the ports, the controlsignal being indicative of activity assignment, to instruct local linkcontrols of the ports to configure link circuits of the ports based uponthe activity assignment via local link controls of the ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a system including a router and a hub totransmit data from one processor card to another;

FIG. 2 depicts an embodiment of a network component such as the routerin FIG. 1 for reducing power consumption by a link;

FIG. 3 depicts an embodiment of a flow chart for a global controller forreducing power consumption by a link; and

FIG. 4 depicts an embodiment of a flow chart for a local controller forreducing power consumption by a link.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of embodiments depicted in theaccompanying drawings. However, the amount of detail offered is notintended to limit the anticipated variations of embodiments, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the embodiments asdefined by the appended claims. The detailed descriptions below aredesigned to make such embodiments obvious to a person of ordinary skillin the art.

Generally speaking, methods and arrangements for power reduction inlinks, such as transmitters and receivers, based upon global decisionssuch as the data transmission frequency, communications media, andtraffic types associated with links, are contemplated. In particular,embodiments take advantage of high-level decisions to reconfigureinternal circuits of links to reduce power consumption. At the global orsystem level, a decision determines the links that are active (i.e.,turned on or off), the data frequency at which the links are operating,and the media through which the links transmit the data. These decisionsare then communicated to the links.

At the local level, the links receive the decisions and each transmitterand receiver pair reconfigures internal circuitry automatically tominimize power based upon the decisions. In some embodiments, the linksmay receive the decisions in the form of power modes. For example, eachlink may receive a control signal indicating that the link should be ina turned off mode, a low power mode, and/or a standard power mode. Infurther embodiments, the links may receive settings such as an on/offsetting, a data frequency setting, and a traffic/media setting. In suchembodiments, the combination of the settings may indicate a power modeso, based upon the settings, the link may selectively adjust or modifythe operation of the internal circuits of the transmitter and receiver.

While specific embodiments will be described below with reference toparticular circuit configurations, power modes, and combinations ofsettings, those of skill in the art will realize that embodiments of thepresent invention may advantageously be implemented with other,substantially equivalent circuit configurations, power modes, andsettings. In particular, the settings may be directly associated with acircuit of a transmitter and/or receiver and may, in some embodiments,indicate particular modifications to the circuit such as a change in theclock frequency for the circuit or a change in the voltage of the highvoltage source, Vdd.

Turning now to the drawings, FIG. 1 depicts an embodiment of a system100 including a router 110 and a hub 140 to transmit data from aprocessor card 105 to a processor card 170. For example, processor card105 may transmit data 107 to processor card 170 via router 110 and hub140. Certain details such as data buffers are not shown explicitly forsimplicity.

Router 110 may determine links through which the data 107 will betransmitted and adjust the operation of link circuits of the links tocorrelate power consumption by the links with characteristics of thedata transmission. Router 110 may include routing table 112, portutilization manager 114, global link control 116, read port 120 andwrite port 130.

Routing table 112 may include a database that contains the currentnetwork topology, to direct packets of a data transmission out theappropriate port. Router 110 may determine the appropriate path 102 ontowhich data 107 should be forwarded from routing table 112 based upon arouting protocol. The routing protocol may also allow the network todynamically adjust to changing conditions by describing how routersshare updated information about the topology. For instance, routingtable 112 may indicate a route 102 from processor card 105 to processorcard 170 via read port 120, write port 130, read port 150, and writeport 160.

Port utilization manager 114 may track availability and usage of portssuch as ports 120, 130, 150 and 160. In the present embodiment, portutilization manager 114 is a global logic for tracking port utilization.In further embodiments, port utilization manager 114 may include logicincorporated into more than one switching chips of router 110 or acombination of global and switching chip level logic. For instance,router 110 may include, e.g., several switching chips, each having 100ports and a port utilization manager that communicates with global linkcontrol. In other embodiments, port utilization manager 114 may includea signal received from logic exterior to router 110.

Based upon the availability of links and the routing information, globallink control 116 may determine that ports 120, 130, 150, and 160 willtransmit data 107 from processor card 105 to processor card 170. Globallink control 116 may then gather information about data 107 to configurelink circuits 124, 134, 154, and 164. In particular, global link control116 may receive data from processor card 105 that describes data 107.For instance, global link control 116 may determine the type of encodingused to encode data 107 and based upon that encoding, determine the typeof data traffic associated with transmitting data 107. For example, areal time video or audio encoding may include long strings of logicalones or zeroes that act as a filler for a video stream to describe thepassage of time. The long strings of logical ones or zeroes are adifficult traffic condition because of the small number of transitionsper unit time, providing clock and data recovery (CDR) loops littleinformation for maintaining the phase of a sampling clock utilized tosample values for each bit in the data stream. Further types of encodingmay produce irregular or sporadic patterns of bit values that are alsodifficult for a receiver to decipher.

In addition to determining the traffic type, global link controller 116may also determine, e.g., a data frequency at which to transmit data107. For instance, global link control 116 may determine a rate at whichprocessor card 105 can transmit data 107 as well as the limitations ondata frequency, or bandwidth, throughout the links between processorcard 105 and processor card 170.

Once global link control 116 determines data transmissioncharacteristics such as the traffic type, the data frequency, and theroute 102 for data 107, global link control 116 may determine a powermode for ports 120, 130, 150, and 160 to correlate power consumptionwith the characteristics or constraints of transmission of data 107.More specifically, when the traffic type is difficult such as the longstrings of logical ones and zeroes or the data frequency is high, morecomplex logic and circuitry of link circuits 124, 134, 154, and 164 maybe powered with higher voltages and clocked with higher clockfrequencies to handle the data transmission. In such situations, astandard power mode may be selected and an indication of the standardpower mode may be transmitted in a control signal to ports 120, 130,150, and 160.

On the other hand, when the traffic type is not difficult, or is simple,and the data frequency is not sufficiently high to justify the use ofthe more complex logic and circuitry of link circuits 124, 134, 154, and164, global link control 116 may transmit a control signal to ports 120,130, 150, and 160 to indicate a low power mode. Further, global linkcontrol 116 may determine that other links (not shown) may not be neededto transmit data 107 so they may be turned off. In some of thosesituations, global link control 116 may also transmit a control signalto turn off and/or reduce power to circuitry of link circuits 124, 134,154, and 164.

Ports such as read ports 120 and 150, and write ports 130 and 160 mayinclude receivers and transmitters designed to respond to controlsignals from global link control 116 by configuring and/orre-configuring link circuits based upon the power mode indicated by thecontrol signals. For example, local link control 122 may receive acontrol signal from global link control 116 to configure link circuit124 to a low power mode and, in response, local link control 122 may,for instance, reduce the amplification of data 107.

Similarly, local link control 122 may receive a control signal fromglobal link control 116 to re-configure link circuit 124 to a standardpower mode. Re-configuring link circuit 124 to the standard power modemay facilitate transmission of data 107 at a higher data frequency.

After port 120 is configured to handle data 107, data 107 may betransmitted from processor card 105 to read port 120. Then, data 107 maybe transmitted through ports 130, 150, and 160 to processor card 170.Advantageously, the ports 120, 130, 150, and 160 consume power at a ratebased upon the routing decision of global link control 116 thatcorresponds to the difficulty in transmitting data 107 through system100.

FIG. 2 depicts an embodiment 200 of a link 219 coupled with a globaldecision device 210 such as router 110 in FIG. 1. Embodiment 200includes a global decision device 210 and a link 219. For example,global decision device 210 makes a routing decision that link 219 is totransmit data at three Gbps instead of ten Gbps. The routing decisioninvolves changing the data frequency of link 219 from ten Gbps to threeGbps and link 219 includes transmitter 220 and receiver 250. Local linkcontrol 222 of transmitter 220 receives the decision as a control signal216 and, in response, turns down the gain of an analog amplifier fordriver 228 and turns off pre-emphasis circuit 226. Similarly, local linkcontrol 252 of receiver 250 receives the decision as a control signal218 and, in response, turns down the analog, receiver amplifier 254 andturns off gain and equalization circuit 256. Advantageously, based uponthe high-level, routing decision of global decision device 210, powerconsumption of link 219 is reduced.

Global decision device 210 may make a global decision regarding anactivity assignment for link 219 based upon information about portutilization 205 and forwarding logic 212, and transmit a control signal216 and 218 to link 219 to indicate the activity assignment for thelink. More specifically, global decision device 210 may be part of aswitch or router and comprise global link control 214 to determine datatransmission characteristics such as the data frequency associated withlink 219, the data traffic for link 219, and the medium through whichdata transmission 240 is transmitted. For example, global link control214 may determine whether to turn off link 219 based upon destinationsassociated with incoming data transmissions and network topologyinformation that associates ports between link 219 and the destinationvia forwarding logic 212. Global link control 214 may select a datafrequency for link 219 based upon a data frequency of an incoming datatransmission. And, global link control 214 may read packet headers ofthe incoming data transmission to determine whether a traffic pattern isa difficult pattern or a simple pattern.

Upon determining whether to turn link 219 off, the data frequency forlink 219, and whether the traffic pattern is simple or difficult, theseoperating parameters may be transmitted in a control signal 216 directlyto transmitter 220 and in a control signal 218 directly to receiver 250.In other embodiments, the operation parameters may be transmitted totransmitter 220 and transmitter 220 may communicate the operationparameters, or an indication thereof, to receiver 250, or vice versa.

The operating parameters resulting from the routing decision may beassociated with a power mode for circuits of link 219 by interpretationlogic 223 of transmitter 220 and interpretation logic 253 of receiver250. More specifically, local link control 222 may receive the operationparameters and utilize interpretation logic 223 to translate theoperation parameters into a power mode for serialization circuit 224,pre-emphasis circuit 226, and driver 228. For instance, when theoperation parameters indicate that link 219 is to be turned off,interpretation logic 223 may indicate that one or more circuits ofserialization circuit 224, pre-emphasis circuit 226, and driver 228should be turned off, declocked, and/or operated at a minimum voltageand frequency.

On the other hand, when the operation parameters indicate that link 219is to be turned on and to operate at a high frequency or transmit adifficult traffic pattern of data, interpretation logic 223 may indicatethat pre-emphasis circuit 226 is turned on and operating at a highcomplexity level, and driver 228 is operating at a high gain. Operatingpre-emphasis circuit 226 at a high complexity level and driver 228 at ahigh gain may involve increasing one or more clock frequenciesassociated with pre-emphasis circuit 226 and driver 228, and increasingthe high voltage source(s) for the circuits in conjunction withincreasing the frequency.

Similarly, receiver 250 may receive the operating parameters eitherdirectly from global decision device 210 via control signal 218, or fromtransmitter 220. In response to receiving operation parametersindicative of a power mode for receiver 250, or a circuit of receiver250, interpretation logic 253 of local link control 252 may determine aconfiguration for a receiver amplifier 254, a gain and equalizationcircuit 256, and a clock and data recovery (CDR) loop 258. For example,receiver 250 may receive operating parameters describing link 219 asbeing turned on with a low data frequency and a simple traffic pattern.In response, receiver amplifier 254 and CDR loop 258 are reduced to aminimum gain and gain and equalization circuit 256 is turned off orreduced to a minimum functionality. In some embodiments, when CDR loop258 is turned off, a substitute CDR loop having minimum functionality isenabled for receiver 250.

Some time after deciding that link 219 should be configured for a lowdata frequency and a simple traffic type, global decision device 210 maydecide to change the activity of link 219. For instance, the datafrequency for data transmissions between transmitter 220 and receiver250 may vary between three Gigabits per second (Gbps) and six Gbps andwhen the data frequency of an incoming data transmission is at six Gbps,global decision device 210 may determine that link 219 should operate ata data frequency of six Gbps to transmit the data 230 from the incomingdata transmission to receiver 250 via data transmission 240. Global linkcontrol 214 generates a control signal 216 for transmitter 220 and acontrol signal 218 for receiver 250. The medium type may be long orparticularly lossy. And the traffic type may complicate clocking thedata transmission, e.g., the data traffic may be very active, oftenswitching between logical ones and logical zeroes at varyingfrequencies. Thus, global link control 214 may determine operatingparameters that indicate a high data frequency and a difficult traffictype. In response, local link control 222 may turn on pre-emphasiscircuit 226 and raise the frequencies and high voltage source forpre-emphasis circuit 226 to maximum ratings. Similarly, local linkcontrol 222 may increase the bias for driver 228 to a maximum.

Receiver 250 may receive the operating parameters via control signal218. In response to control signal 218, local link control 252 mayincrease the bias for receiver amplifier 254 to a maximum, increase thecomplexity, high voltage source, and/or frequencies for gain andequalization circuit 256, and implement a circuit for CDR loop 258having second and third order frequency tracking.

Upon adjusting the activity of link 219, serialization circuit 224serializes data 230, clocking the data at six Gbps, and, in manyembodiments, pre-amplifies the serialized data based upon inputspecifications for pre-emphasis circuit 226. In many embodiments, forinstance, serialization circuit 224 includes a low frequency clocksource having low jitter (to maximize the sampling window for the data)and a multiple phase output. The rising and/or falling edges of themultiple phases are utilized to clock parallel inputs of data 130 into asingle, six Gbps data stream.

Pre-emphasis circuit 226 may utilize a finite impulse response (FIR)equalizing filter to cancel or at least reduce frequency-dependentattenuation such as attenuation caused by the skin-effect resistance ofcopper wire when copper wire is the medium through which datatransmission 240 is transmitted. Pre-emphasis circuit 226 accentuatesthe high frequency components of the data signal to at least partiallyalleviate the effects of inter-symbol interference (ISI).

Then, driver 228 drives data transmission 240 across a medium such as acopper wire or an optical fiber. In some embodiments, for example,driver 228 may include a Fibre Channel driver and data transmission 240may be transmitted through a channel of a fiber optic cable.

Receiver 254 receives data transmission 240 from driver 228 andpre-amplifies data transmission 240 for gain and equalization circuit256. Gain and equalization circuit 256 amplifies data transmission 240and accentuates the high frequency components to attempt to increase thesampling window for the data. Then, CDR loop 258 samples the data fromthe data signal, compares the phase of the sampling clock to the phaseof the data transmission 240 and adjusts the sampling clock accordingly.When second order and third order frequency tracking circuits areincluded in CDR loop 258, second and third order corrections are made toadjustments of the sampling clock phase. For example, initial samplesfrom the data transmission indicate instantaneous, high frequencychanges to the phase of the data transmission. Second order and thirdorder frequency tracking circuits observe and correct for lowerfrequency changes in the phase of data transmission 240. Once CDR loop258 samples the data transmission 240, the determined values of the bitsare output as data 260.

Referring now to FIG. 3, there is shown an example of a flow chart 300for a global controller such as router 110 of FIG. 1. The globalcontroller may determine activity assignments for each link and theactivity assignments may be communicated to the local controller of thelink in the form of one or more power modes or one or more settings thatare indicative of power modes for link circuits such as circuits forpre-emphasis, amplification, equalization, and CDR. Flow chart 300begins with turning off unnecessary links (element 310). Morespecifically, a high-level decision device determines which links toturn off based upon forwarding logic such as a routing table and thecurrent utilization of ports associated with the links.

After the unnecessary links are turned off, the high-level decisiondevice assigns destination nodes to active links to utilize the linksfor different, incoming data transmissions based upon forwarding logic(element 320). Selecting destination nodes for the active links mayinvolve assigning particular incoming data transmissions to portsassociated with particular active links. In further embodiments,assigning destination nodes to a link involves selecting a mediumthrough which the link will transmit data. Selecting the medium may bemore prevalent, for example, in optical routers.

Once the destination nodes are assigned to ports of active links,characteristics of a data transmission associated with the ports ofactive links are collected to determine an activity assignment for thecorresponding active link (element 330). The activity assignment maydescribe, for instance, the data frequency for the data transmission,and the media type and traffic type of the data transmission. In someembodiments, the activity assignment may be represented by a power mode.

The activity assignment is then transmitted to the link and if there aremore links for which the global decision device determines an activityassignment (element 345), characteristics associated with the datatransmission for those links are determined (element 330) andtransmitted (element 340).

Referring now to FIG. 4, there is shown an example of a flow chart 400for local controller such as transmitter 220 or receiver 250 as shown inFIG. 2. The local controller may include a local link control such aslocal link control 222 or local link control 252 in FIG. 2. For example,the local controller may receive an activity assignment from ahigh-level decision device such as a router that determines what datawill be transmitted via a link associated with the local controller, andwhat medium will be used to transmit that data to a destination.

Flow chart 400 begins with receiving an activity assignment (element410) for a link. The activity assignment may indicate a data frequency,a media type and/or a traffic type for a data transmission to beprocessed by one or more link circuits associated with the link.

Based upon the activity assignment, the power modes of each of the oneor more link circuits may be determined (element 420). For instance,when the activity assignment includes a data frequency and the datafrequency is a relatively high frequency, link circuits may beconfigured to operate in a high power consumption state to process thehigh data frequency. Similarly, if the activity assignment includes anindication that the traffic type is difficult, link circuits may beconfigured to operate in a high power consumption state to amplify,pre-emphasize and/or equalize the data transmission.

Upon determining the power mode for the link circuit, the link circuitis configured based upon the power mode to adjust power consumption(element 430). Whether the power consumption of the link circuit is highto accommodate high data frequencies or difficult traffic types, thelink circuit is dynamically configured to, advantageously, consume anamount of power related to the complexity of the data transmission.

Then, if the link includes additional link circuits, the additional linkcircuits are configured based upon the activity assignment communicatedby the high-level decision device (element 440).

It will be apparent to those skilled in the art having the benefit ofthis disclosure that the present invention contemplates methods andarrangements for power reduction in links, such as transmitters andreceivers, based upon global decisions such as the activity, datatransmission frequency, communications media, and traffic typeassociated with links. It is understood that the form of the inventionshown and described in the detailed description and the drawings are tobe taken merely as examples. It is intended that the following claims beinterpreted broadly to embrace all the variations of the exampleembodiments disclosed.

1. An apparatus to retransmit a data transmission between a first deviceand a second device via intermediate links, the apparatus comprising: aglobal link control to determine ports of the intermediate links totransmit the data transmission to a destination device; to determine anactivity assignment for the ports of the multiple links based uponforwarding logic, wherein determining the activity assignment comprisesdetermining a data frequency, traffic type, and medium type for the datatransmission; and to transmit a control signal with the activityassignment to local link controls of the intermediate links associatedwith the data transmission; a first port to communicatively couple witha transmitter of the first device via a first data transmission mediumto form a first intermediate link of the intermediate links, the firstport comprising a first link circuit to couple to the first datatransmission medium, to receive the data transmission from the firstdevice, and a first local link control of the local link controlsresponsive to the control signal from the global link control toconfigure the first link circuit to operate in a first power mode ofmultiple power modes associated with the first link circuit based uponthe activity assignment; and a second port to communicatively couplewith a receiver of the second device via a second data transmissionmedium to form a second intermediate link of the intermediate links andwith the first port to retransmit the data transmission, the second portcomprising a second link circuit to couple to the second datatransmission medium, to transmit the data transmission to the seconddevice, and a second local link control of the local link controlsresponsive to the control signal from the global link control toconfigure the second link circuit to operate in a second power mode ofmultiple power modes associated with the second link circuit based uponthe activity assignment.
 2. The apparatus of claim 1, wherein the firstlink circuit comprises a clock and data recovery loop, wherein anability of the clock and data recovery loop to track changes in a phaseof the data transmission varies between the first power mode and otherof the multiple power modes associated with the first link circuit. 3.The apparatus of claim 1, wherein the first link circuit comprisescircuitry that is configurable to adjust amplification of the datatransmission.
 4. The apparatus of claim 1, wherein the first linkcircuit comprises a gain and equalization circuit being configurable viathe first local link control in response to the control signal tocompensate for attenuation and distortion based upon a medium associatedwith the data transmission.
 5. The apparatus of claim 4, wherein firstlocal link control comprises interpretation logic to reconfigure thefirst link circuit in response to the control signal, wherein thecontrol signal is related to a traffic type associated with the datatransmission.
 6. The apparatus of claim 1, wherein the first local linkcontrol comprises interpretation logic to adjust an operating voltageand frequency for the first link circuit in response to an indication bythe control signal of a data frequency for the data transmission.
 7. Theapparatus of claim 1, wherein the second link circuit comprises aserialization circuit that is configurable via the second local linkcontrol to process the data transmission in accordance with a datafrequency indicated by the control signal.
 8. The apparatus of claim 1,wherein the second link circuit comprises a pre-emphasis circuit that isconfigurable via the second local link control in response to thecontrol signal.
 9. The apparatus of claim 1, wherein the second locallink control is to reconfigure the second link circuit in response tothe control signal, wherein the control signal is indicative of a lengthof a medium for the data transmission.
 10. The apparatus of claim 1,wherein the second local link control comprises interpretation logic toselect the second link circuit and the second power mode for the secondlink circuit based upon the control signal.
 11. The apparatus of claim10, wherein the interpretation logic comprises a table to associate thesecond power mode with a data frequency, wherein the control signalindicates the data frequency.
 12. An apparatus, comprising: forwardinglogic to associate ports with multiple links between an origin and adestination for a data transmission to transmit the data transmissionvia the multiple links to the destination, each of the multiple links tocomprise a first port with a transmitter communicatively coupled with areceiver of a second port via a data transmission medium; and a globallink control coupled with the forwarding logic to determine an activityassignment for the ports of the multiple links based upon the forwardinglogic, wherein determining the activity assignment comprises determiningthe data frequency, traffic type, and medium type for the datatransmission to transmit a control signal to the ports, the controlsignal being indicative of activity assignment, to instruct local linkcontrols of the ports to configure link circuits of the ports based uponthe activity assignment via local link controls of the ports.
 13. Theapparatus of claim 12, further comprising a local link control,responsive to the control signal, to configure the circuitry associatedwith at least one of the multiple links to operate in a power modeassociated with the control signal.
 14. The apparatus of claim 13,wherein the local link control comprises part of a receiver and isdesigned to adjust power consumption by the at least one of the multiplelinks by selecting the power mode, wherein the power mode maintains adata throughput.
 15. The apparatus of claim 13, wherein the local linkcontrol comprises part of a transmitter, the transmitter being adaptedto deactivate a gain and equalization circuit based upon the controlsignal.
 16. The apparatus of claim 13, wherein the local link control isadapted to change an operating frequency and an operating voltage forthe circuitry based upon the control signal.
 17. The apparatus of claim12, wherein the global link control is designed to communicate a routingdecision of a router for the ports of the multiple links in the controlsignal to the local link controls of the multiple links, wherein therouting decision determines a data frequency, a traffic type, and amedium type for the data transmission, to configure the ports inaccordance with the routing decision.